In the above-described technical field, when a tape material having a layer for an intended purpose is transported, the substrate and the coating layer of a tape material are provided with different properties to ensure the product quality that satisfies its intended purpose and to allow easy manufacturing. The physical properties of the front and the back surfaces of the tape material in this sense include an elastic modulus, a friction coefficient, surface roughness, and adhesion strength. Therefore, the correlation between these properties and the surface of a pair of rollers that nip and transport the tape material must be a due consideration.
When the rape material is nipped and transported by a pair of rollers, an excess nip force may physically damage the coating layer and/or substrate of the tape material and cause functional failure of the final product. For example, in the case of a photo-sensitive material having the emulsion layer on a substrate, excessive compression onto an emulsion layer causes pressure fogging. In the case of a magnetic material having magnetic material on a substrate, excessive compression on a magnetic layer causes fissure peel, resulting in failure in data-reproducing. A thermal recording tape causes printing failure owing to peel of thermal paint.
To ensure the requirements of stable transportation and positive quality control, Japanese Patent Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 118832/1979 is focused on a friction coefficient and recommends that an average roughness Ra of the roller surface be from 2 to 40 .mu.m. According to the arrangement in Japanese Patent O.P.I. Publication No. 153360/1985, a free roller whose surface having a larger coefficient of friction is pressed onto a coating layer (photographic emulsion layer), while driving rollers of a smaller friction coefficient are pressed onto the back face of the tape material, wherein the revolutions of the driving rollers are gradually larger toward the direction of tape material transportation, thereby excessive friction and transportation tension on the coating surface are eliminated in order to prevent transportation-induced product failure.
In that patent specification, however, the nip pressure that is exerted between nipping roller pairs which significantly affects stable transportation is not specified; there is no clear correlation between the maximum nip pressure that does not cause damage to the tape material, the elastic modulus to be given to the tape material surface, and the elastic modulus that is given to the nipping roller surface. Accordingly, it is impossible with this arrangement to increase the nip pressure in order to ensure transportation stability, and high-speed operation.